Class 3: Anatomy of a Screw Up

Thoughts on Making Mistakes

The plan for the night was to finish routing the channel for the soundhole rosette and then to set and glue the rosette into the soundboard.  The other activity was to bend my sides.  Things started out well as I routed out the channel in three passes with the circle cutting jig set to a depth of about .075" inches, a little bit shy of the thickness of the maple piece.  For each pass I first routed a channel in the MDF work board, then moved over to the top of the soundboard.  The first pass went through the middle of the channel, the second to the inside radius, and the third to the outside radius.  After the second and third passes in the MDF, I tested the fit of one of the rosette pieces along with two strips of purfling.  After the third pass everything looked to fit well.

The only remaining step was to rout a final circle through the thickness of the soundboard to cut out the actual sound hole.  After adjusting the depth and radius, I made the final pass, but it was clear from a little way in that something was wrong.  Turns out I forgot to turn the locking nuts on the jig, so as I cut with the router, the radius of the cut kept increasing.  The result: a spiral soundhole that cut up to the edge of the rosette channel.  After at least 5 passes with the router to cut out the rosette and dig the channel, on the very last pass I forgot a basic step.

Here's a closer shot of the piece that came out.  This should be a perfect circle.

Here's where it also gets interesting working with Edward.  His first instinct was that I might need to start a new soundboard, but after closer inspection he thinks it can be saved.  For now, what I'm trying to do is to glue the rosette into the channel, surrounded by the two purflings.  After it has glued, we will finish removing the remaining wood on the inside edge of the sound hole until the outside purfling becomes the edge of the sound hole.  At that point, we may look at adding an additional strip of wood to give a little more reinforcement to the sound hole.  It should look quite nice and may result (?) in a little more volume from the guitar.

I appreciate Edward's approach to problems.  Generally, mistakes are  looked at as part of the course of developing skill rather than as evidence of imperfection.  While we are trying to make the best guitars we can in the class, by being careful and using the skills we have, it is understood that the experience of learning and developing new skill is part of the journey and that the completion of a single instrument should not be seen as the end of our travels.  This attitude which runs through his classes is probably what has made this process so enjoyable for me.  It stresses the chance to continue developing rather than the completion of products.  This is not to say that there is no interest in completing the projects, but the feeling of growth is in many ways as important.

So, I took Edward's advice and continued using what I had - here's the rosette being glued in, covered by a piece of wax paper and a caul to compress it evenly.  The edge of purfling where the channel has no inner wall is held against a few finish nails tacked into the piece of MDF.  I'll have to see what it looks like after the break for Thanksgiving.

Here's a shot of a similar rosette done by another student.  This is how mine was intended to look.The strip of spruce on the inside of the rosette is what will be missing.








Side Bending

I also bent the sides of my guitar and the binding strips.  I think they look pretty nice:

The first side took some additional manipulation to get set evenly in the mold, as a result it was essential bent twice.  This might be why there are some compression marks along the waist.  Edwards thinks that these will mostly sand out.  More adventures.

It was also interesting to contrast my experience in working on this project with a conversation at lunch with a friend who's late father was a serious luthier.  Apparently he was a woodworker and a machinist with much passion for the craft.  The type of craftsman who honored his tools, sought out his own materials and rarely took shortcuts.  Almost all of his work was done without power tools - planes were apparently his passion.  Although, he apparently did not make his own rosettes (another lesson here?).  I would love to see some of his work. 

However, sitting at lunch with my friend and his brother, both of whom were brought up in their dad's shop, neither could profess any interest in woodworking on their own.  Apparently their father had always viewed their efforts as instructional opportunities.  Praise was never available.  As a result, neither ever developed any enjoyment for the activity.  To put it all simply, attitude seems to be important.

Class 2: Rosette and Preparing to Bend Sides

Soundhole Rosette

I continued to work through a couple of iterations of the radii I would need to define the inside and outside curves of the rosette. 

These were laid out on paper and then on the piece of spalted maple.  The maple was taped with double sided tape onto a piece of MDF in order to be cut with a router with a circle cutting jig.  The router is equipped with a downward spiral flute bit - the downward spiral helps to ensure that the edges of the cut are not torn upward.

Afterward, the resulting circle had to be carefully separated from the MDF in order not to break the ring; inevitably,  however, it did break into a few pieces.  Once broken, however, it is easily reassembled.  Additional 'grain' can be added by using a pen to color the would around the fractures, but I'm skipping that step.

Here is the ring (now in 4 parts) ready to be laid into the soundboard next week.  In order to define the channel into which the pieces will be inscribed a channel will be routed in the sound board.  Layout of this channel has to also allow for room for an inside and outside strip of purfling as well as the glue joints between the wooden rosette ring.

Edward estimates that each glue joint adds .005" to the required channel with, and the purfling strips measure .060" across.  The channel width, with two purfling strips and associated glue joints, must be a total of .130" wider than the ring.  Measurement of the ring is taken off of the MDF on which the ring was cut out.  The measurements are then increased the required  amount and then laid out on the top.  A dry run to sizing the channel will also be done on the MDF board on which I am working.  The ring is about .080" thick, so we need to get the router bit depth a little shy of that (about .070") so that the rosette sits a little proud of the soundboard prior to thickness sanding.

Bending

Half of the class bent the sides for their guitars today.  I'll do mine next week, but got them set up with the binding strips in preparation.

Each of the two sides was taped up with a binding strip on the top and bottom so that the bindings can be bent together with the side in order to have the same curve.

The bending process begins with soaking the wood for several hours.  Each side is then heated in a sandwich made of the side, encased by two pieces of sheet metal, encased by heating blankets (see the first picture in the sequence below).  These blankets can get north of 500 degrees, so the sides heat quickly and give off steam.  After heating for a while, the whole package is firmly forced into the mold then clamped together for the sides to cure.

Here's the sequence, demonstrated by Edward

Edward uses the following timing in this sequence:

1. Heating blankets are plugged in and the side is heated for 2.5 minutes.
2. While still heating (use gloves), the side is forced into the mold.
3. At the 4 minute mark, the heating blankets are turned off, so as not to overheat and burn out over time.  LMI recommends using the blankets with a rheostat or other control so as to not overheat and burn out, but Edward uses these timings based on full throttle.
   
4. After a 30 seconds, (4.5 minute mark), the blankets are turned on for another 45 to 60 seconds.
5. At about 5:15 or 5:30, the blankets are unplugged and the sides are left in the frame for an hour before unclamping.

All three sets done last night seemed to unclamp and come out fine.  Next week, I'll be bending my sides and finishing the channel for the rosette so that it can be glued up.

Design details

Soundhole Rosette
This weeks homework is to come up with a design for the soundhole rosette.  The rosette will be cut out of a piece of spalted maple and surrounding by purfling strips.  So the design is a fairly simple affair: working out the width of the rosette and the offset from the soundhole.  The proportions I'm looking at are shown below (not to scale)

The soundhole diameter is about 3-3/4", the rosette will be offset a quarter inch and measure just under 1/2" across.  I'm wondering about breaking it into 4 quarters (as shown above) with additional purfling strips.

Headstock
I've also been thinking about the headstock design.  I'd like to use another piece of walnut for the plate and try to due some type of inlay either in wood or shell abalone.  It will have to be something simple, maybe a very basic compass rose.  I'll need to work up some designs, although this is probably a couple months out.

First Class

Initial Thoughts
Tonight was the initial class.  The first half was spent on an orientation to Edward's shop and teaching

process.  From there we started talking about design issues and the role of materials - wood - in affecting a design.  We discussed some of the physical qualities of wood - it's response to moisture, tension and vibration and the importance of how wood is cut.  Guitar woods need to have straight, continuous grain, so boards are almost always quarter saw (here are some nice images of a quarter sawn log).

The art of building a guitar is to bring the materials together in a design that is just strong enough to resist the tension of the strings (up to 150 lbs/psi for a steel string guitar) without falling apart.

For me, on this project, the other design key is size.  The OM guitar that I'm starting on has a smaller body than a dreadnought, emphasizing the treble and less bass and making it more appropriate for finger picking.  I'm hoping that the walnut also helps to bring out a strong voice for the treble while still providing a solid bass.

Materials

Here is a preview of the woods that I am using for this class.  The top is Engelmann Spruce which has consistent color and grain.  For the back and sides I am using Peruvian Walnut which is a relatively inexpensive tone wood with consistent grain and should bend easily.  I'm also hoping to get strong treble tones from it.

The bindings will be Koa, although I debated using some darker Rosewood to get more contrast with the top.  Spalted maple will be the basis of the soundhole rosette.

Top, back and Side Layout
Layout began with tracing the provided template onto the back and top.  The template is registered off the center to ensure that the jointed seam in both the top and bottom becomes the center of the top and side pieces.

Here are the back and top with the OM shape drawn onto them.  These were then rough cut on the bandsaw.

First cuts made and it already looks like a guitar.

Next the sides needed to be laid out.  The trick is to understand which end will go where (butt or neck) and to preserve the bookmatched grain.  The sides are marked up as shown in the diagram below.

The pieces are then taped together with the butt ends and neck ends together so that a single template can then be laid across both.  Key is to making sure the top edge is kept together.  This edge will match to the top of the guitar in one of the few right angles in the project.

Once laid out these pieces are also cut to depth following the curve of the template.  The initial pieces are now all roughed out


Next week we will be working on cutting out the rosette for the soundhole and preparing to bend the sides.  Homework this week is to figure out the sizing and location of the rosette in relationship to the soundhole, which has a diameter of 3.75 inches.

Kick off

If anyone is interested, I'm starting this blog off in order to have a place to organize my notes and photographs from my second class with Edward Dick at the Colorado School of Lutherie. Two years ago I stumbled on Edward's class while looking for something more productive to which to apply myself. I loved the class, both the learning of skill and the opportunity to build an instrument (a dreadnought steel string guitar similar to a Martin D-28). I was convinced that this was a hobby that I wanted to continue with.

The opportunity has arisen, so tomorrow I start working on an intermediate level project. This one will be targeted to be more of a finger style guitar, with Walnut back and sides (maybe something like this, minus the cutaway). Anyways, the purpose of this blog won't be so much introspection or attempts to generate comments, but primarily a way to make sure that I put together my notes on the building process in such a way that I can access them again.